The present invention relates to electromotors in general, and more particularly to an electromotor with a laminated stator in which a stator ring has inwardly protruding pole pieces The pole pieces have a substantially T-shaped cross section with a shaft or foot portion projecting from the stator ring and a head portion projecting from both sides of the shaft portion and having its surface facing the rotor curved to form a cylindrical surface having a radius slightly greater than the outer radius of the rotor with which it cooperates, and being slightly spaced therefrom. Relevant stator coils are mounted on the shaft portions of the pole pieces in such a manner that they fill the space behind the rear sides of the projecting parts of the head portion.
The easier way of shaping the pole pieces is to stamp them out, together with the remaining portions of the stator laminations, from the plate material used for manufacturing of the laminated stator, such that the pole pieces will appear as inwardly projecting, integrated parts of the stator ring. This, however, incurs the essential drawback residing in that the stator coils will be mounted by being heeled over the broader head portions of the pole pieces and then narrowed about the shaft portions. However, it has been difficult to mount the coils on the pole pieces in such a way and even more difficult to change them when necessary.
It has long ago been suggested and practiced to provide the pole pieces as separate units from the stator ring and to mount the coils with a narrow shape about the shaft portions, which was easier because they were placed on the shaft portions of the poles from the narrow ends thereof, that is without being heeled over the head portions, and the coil carrying pole pieces were then mounted on the inside of the stator ring and fixed thereto in any suitable manner. The connection of the pole pieces to the stator ring could even be easily releasable, whereby it was possible to replace a burnt coil with a new one in a relatively simple manner.
However, there are considerable problems connected with the production and particularly securing of the separately made laminated pole pieces to the stator ring. Ideally the single lamination for the pole pieces should be formed in connection with the stamping out of each single stator lamination, by cutting off the inwardly projecting pole portions from the ring area along their base connection with the inner side of the stator ring, i.e. along or rather across the roots of their shaft portions. However, with this technique it is difficult to achieve an accurate and non-problematic mounting of the assembled, rod-like pole pieces on the interior side of the likewise assembled stator ring. It has been proposed to fasten the pole pieces by means of bolts introduced from the outside thereof. However, such fastening would require accurately drilled radial holes in the assembled lamination material and cutting threads in the holes of the pole pieces, which would amount to a quite difficult working. Moreover, it may have quite serious consequences for the entire motor if the spanner bolts of just a single pole piece would get loose, e.g. in case of a less qualified mounting or repair.
Furthermore, fastening of the above-described nature would also require the provision of radial passages through the stator ring or cylinder, which is undesired as this would facilitate penetration of moisture into the rotor area.
In order to avoid these problems it has already been proposed to shape the pole pieces and the single laminations thereof with protruding, narrow foot portions fitting into a corresponding recess in the inner wall of the stator ring, a corresponding recess being formed in each single stator lamination, to thereby ensure a very accurate positioning of the pole pieces, and, at the same time, achieve a safer fastening of the pole pieces using locking means that are active at the radial or lateral sides of the foot portions of the pole pieces, respectively. Such locking means can be formed by locking rods inserted through axially extending holes or opposed half holes formed in the adjacent side faces.
However, even this solution is problematic because it is hardly possible to form both the foot portions and the corresponding recesses in one operation or by stamping from one common lamination plate in such a manner that the parts can later be easily joined to each other. The foot portions should be just slightly narrower than the recesses, and for this to be possible the pole piece laminations, in practice, should be stamped out from plate or lamination members other than those, from which the stator ring laminations are stamped out, this incurring a heavy excess consumption of lamination plate material.